Many conventional multi-function exercisers are not portable because they are too bulky to be carried. Conventional portable exercisers have several drawbacks stemming from the use of restoring force as resistance. The restoring force can be provided by a spring or elastic strap. When the spring or strap is deformed there is a risk that control of the device will be lost and an injury may be incurred. For instance, if the spring, handle, or strap broke or the user lost his grip on the handles, the conventional exerciser would have a violent change in resistance. Another drawback of conventional portable exercisers is that the restoring force is not constant; it changes as the spring or strap is stretched. A variable resistance does not allow the user to employ a smooth motion or experience a smooth feeling when employing the device.
Another drawback of conventional portable exercisers is that the restoring force can pinch the skin of the user. The spring or elastic strap is designed for use by a person of a specific size and cannot be comfortably employed by a user of a different size. Other conventional devices exercise only one group of muscles.